1. Field of the Invention
The present invention relates generally to test and diagnosis device for a data processing unit and more specifically to maintenance circuits incorporated within such a device for enabling the detection and localization of abnormal conditions within such a unit via another data processing unit.
2. Description of the Prior Art
The increasing complexity of systems of data processing and especially of the central units contained in these systems renders more and more difficult the execution of their checking and maintenance by specialist technicians. In order to react as rapidly as possible to trouble, the technicians must be furnished with equipment which can be connected to plug-in units of the machine needing repair in order to carry out predetermined tests. These tests are effected by numerous manual operations, often lengthy, which cause a great loss of time.
In order to correct this loss of time, means have been developed for detecting trouble automatically and localizing them at the level of the various functional units of the system during the course of data processing, thus facilitating the work of the repairman. Means have likewise been developed for testing a system before it starts to carry out a data process, that is, at the time the system starts. Such means are described in the U.S. Pat. application Ser. No. 450,936, filed Mar. 13, 1974, entitled "Testing System For A Data Processing Unit" by Gilles Jean Marcel Bottard, which corresponds to the French Pat. appliction No. 73 09558, filed on the Mar. 16, 1973. These means prevent data processing under abnormal conditions of operation of a system. In this manner time may be gained, since trouble is reacted to immediately and before any processing is started.
Localization of trouble at the level of a functional unit of the system facilitates the repairman's work, but the task of looking for a fault at the level of one element of the functional unit in question remains and may take a long time. In order to reduce by an appreciable degree the time of intervention of the repairman, means have been developed consisting in carrying out a diagnosis by the execution of tests on all the elements of a functional unit in trouble, which enable all the symptoms of a fault to be collected. If a dictionary of faults has been previously established by simulation of all foreseeable faults, it is possible to localize a "hardware" fault at the level of the smallest interchangeable element of a data processing unit by identification of the symptoms collected.
Certain systems can test themselves automatically by executing programs and microprograms of tests written in the permanent memory of their central unit. In the case of certain configurations in which a relatively large number of peripheral units are connected to the central unit of a system, it is necessary to reserve a large place in the memories for the execution of tests. Under these conditions there is a need to provide for the possibility of carrying out complementary tests under control external to the system in question. These tests can be made either manually by a maintenance panel or automatically by a test and diagnosis device connected to the system to be tested. Such devices are in general costly and too specialized to be employed, for example, in the course of manufacture. In order to connect such a device to the system to be tested, there must be provided special means of adaptation which change depending upon the type of system to be tested. A type of adapter has been developed as an element of a universal system for enabling communication over great distances with a number of external devices by means of a communication terminal. An adapter of this type is designed, for example, for sending test data to the system to be tested at rest. This adapter localizes the faults by comparison of the data resulting from the test of the system with reference data sent by the external test device. The various data transfers are carried out by manual commands from a maintenance panel associated with the system to be tested. Such adapters do not enable complete and automatic test of all of the central unit of a system nor an automatic diagnosis, since the state signals of the various registers of the unit to be tested are conveyed through the maintenance panel. This is so even in the case of a transmission towards an external device connected to the adapter.